In order to detect objects or surfaces, use is frequently made of methods which gradually scan the topography of a structure, such as a building, and record the same in the process. Here, such a topography constitutes a sequence of points that is coherent and describes the surface of the object or else a corresponding model or a description of the surface. A familiar approach is scanning by means of a laser scanner, which in each case detects the physical position of a surface point by the distance to the targeted surface point being measured by the laser and this measurement being linked with the angular information from the laser emission. From this distance and angular information, the physical position of the respectively detected point can be determined and the surface can be measured continuously. In many cases, in parallel with this purely geometric detection of the surface, it is also possible to make an image recording by means of a camera, which, in addition to the visual overall view, also provides further information, for example with reference to the surface texture.
In addition, other measuring devices such as profilers, total stations or laser trackers are generally likewise suitable for such scanning operations, wherein this is usually implemented via coaxial distance measuring elements or scanning elements and computing, control and storage units in the respective device. Depending on the configuration level of the measuring device, in addition motorization, for example of an aiming or sighting device—in the case of use of retro-reflectors (for example from an all-round prism) as target objects—can be integrated as means for automatic target searching and tracking.
Scanning measuring devices according to the prior art make it possible for a user to detect large surfaces and objects with relatively little expenditure of time—depending on a desired point-to-point resolution—completely and possibly with additional object information. In this case the devices are typically configured in such a way that primary point clouds with a large number of measuring points can be detected, and this detection is carried out with sufficient accuracy.
To this end, a very fast-rotating laser beam is emitted into the surroundings and the reflected light signal is evaluated in an appropriately frequency-based manner. Usually, this “scanning” laser beam rotates about a fast axis and about a slow axis (orthogonal to the first axis), which means that scanning is possible in all three spatial angles. In particular, the fast-rotating axis needs a rugged and exact mounting on account of the high rotational speeds. In this case, the precision must remain constant over a relatively long time period and over wide temperature ranges.
Previous total stations are operated with a plain bearing with regard to the elevation axis. In previous laser scanners, a conventional fixed/floating mounting is normally used, which is able to ensure a constant preload at most by additional elements, such as springs, sealing rings and further resilient bodies, also being incorporated as an integral constituent part of the mounting.
By means of these additional elements, in the case of thermally induced expansion of the bearing system, the floating bearing is kept in position in such a way that the mounting does not distort. These conventional mountings are complicated in planning and construction, need more parts and overall space and do not offer optimal rigidity.
The change in the preload within an operating temperature range is undesired since, in the event of an enlargement of the bearing play, the results of the measurement become inaccurate and since, in the case of too high a bearing preload, the increased friction leads to a greater power demand, which in particular is critical for battery operated, mobile measuring devices with a limited power capacity.